Implement mg_http_parse_header2()

Which is a replacement of (deprecated) `mg_http_parse_header`, but,
similarly to `asprintf`, allocates a new buffer if the client-provided
one is not large enough.

Also use it throughout mongoose code, and thus some header-related
limitations are removed; in particular,
https://github.com/cesanta/mongoose/issues/813 is fixed.

CL: Mongoose Web Server: Deprecate `mg_http_parse_header()` and implement `mg_http_parse_header2()` instead, which allocates a new buffer if the client-provided one is not large enough (similarly to `asprintf`).
CL: Mongoose Web Server: Fix limitations of header value lengths, e.g. when parsing authentication headers such as nonce, etc.

PUBLISHED_FROM=c75b1bbbbdb294ea85075ce69b1368f115fdd1ef

docs/c-api/mg_http_server.h/intro.md

@@ -10,6 +10,7 @@ items:
   - { name: mg_get_http_var.md }
   - { name: mg_http_check_digest_auth.md }
   - { name: mg_http_parse_header.md }
+  - { name: mg_http_parse_header2.md }
   - { name: mg_http_reverse_proxy.md }
   - { name: mg_http_send_error.md }
   - { name: mg_http_send_redirect.md }

docs/c-api/mg_http_server.h/mg_http_parse_header.md

@@ -7,17 +7,9 @@ signature: |
                            size_t buf_size);
 ---
 
-Parses the HTTP header `hdr`. Finds variable `var_name` and stores its value
-in the buffer `buf`, `buf_size`. Returns 0 if variable not found, non-zero
-otherwise.
+DEPRECATED: use mg_http_parse_header2() instead.
 
-This function is supposed to parse cookies, authentication headers, etc.
-Example (error handling omitted):
-
-    char user[20];
-    struct mg_str *hdr = mg_get_http_header(hm, "Authorization");
-    mg_http_parse_header(hdr, "username", user, sizeof(user));
-
-Returns the length of the variable's value. If buffer is not large enough,
-or variable not found, 0 is returned. 
+Same as mg_http_parse_header2(), but takes buffer as a `char *` (instead of
+`char **`), and thus it cannot allocate a new buffer if the provided one
+is not enough, and just returns 0 in that case. 
 

docs/c-api/mg_http_server.h/mg_http_parse_header2.md

+---
+title: "mg_http_parse_header2()"
+decl_name: "mg_http_parse_header2"
+symbol_kind: "func"
+signature: |
+  int mg_http_parse_header2(struct mg_str *hdr, const char *var_name, char **buf,
+                            size_t buf_size);
+---
+
+Parses the HTTP header `hdr`. Finds variable `var_name` and stores its value
+in the buffer `*buf`, `buf_size`. If the buffer size is not enough,
+allocates a buffer of required size and writes it to `*buf`, similar to
+asprintf(). The caller should always check whether the buffer was updated,
+and free it if so.
+
+This function is supposed to parse cookies, authentication headers, etc.
+Example (error handling omitted):
+
+    char user_buf[20];
+    char *user = user_buf;
+    struct mg_str *hdr = mg_get_http_header(hm, "Authorization");
+    mg_http_parse_header2(hdr, "username", &user, sizeof(user_buf));
+    // ... do something useful with user
+    if (user != user_buf) {
+      free(user);
+    }
+
+Returns the length of the variable's value. If variable is not found, 0 is
+returned. 
+

examples/cookie_auth/cookie_auth.c

@@ -59,20 +59,29 @@ static int check_pass(const char *user, const char *pass) {
  */
 static struct session *get_session(struct http_message *hm) {
   struct mg_str *cookie_header = mg_get_http_header(hm, "cookie");
-  if (cookie_header == NULL) return NULL;
-  char ssid[21];
-  if (!mg_http_parse_header(cookie_header, SESSION_COOKIE_NAME, ssid,
-                            sizeof(ssid))) {
-    return NULL;
+  if (cookie_header == NULL) goto clean;
+  char ssid_buf[21];
+  char *ssid = ssid_buf;
+  struct session *ret = NULL;
+  if (!mg_http_parse_header2(cookie_header, SESSION_COOKIE_NAME, &ssid,
+                             sizeof(ssid_buf))) {
+    goto clean;
   }
   uint64_t sid = strtoull(ssid, NULL, 16);
-  for (int i = 0; i < NUM_SESSIONS; i++) {
+  int i;
+  for (i = 0; i < NUM_SESSIONS; i++) {
     if (s_sessions[i].id == sid) {
       s_sessions[i].last_used = mg_time();
-      return &s_sessions[i];
+      ret = &s_sessions[i];
+      goto clean;
     }
   }
-  return NULL;
+
+clean:
+  if (ssid != ssid_buf) {
+    free(ssid);
+  }
+  return ret;
 }
 
 /*
@@ -91,7 +100,8 @@ static struct session *create_session(const char *user,
   /* Find first available slot or use the oldest one. */
   struct session *s = NULL;
   struct session *oldest_s = s_sessions;
-  for (int i = 0; i < NUM_SESSIONS; i++) {
+  int i;
+  for (i = 0; i < NUM_SESSIONS; i++) {
     if (s_sessions[i].id == 0) {
       s = &s_sessions[i];
       break;
@@ -176,7 +186,8 @@ static void logout_handler(struct mg_connection *nc, int ev, void *p) {
 /* Cleans up sessions that have been idle for too long. */
 void check_sessions(void) {
   double threshold = mg_time() - SESSION_TTL;
-  for (int i = 0; i < NUM_SESSIONS; i++) {
+  int i;
+  for (i = 0; i < NUM_SESSIONS; i++) {
     struct session *s = &s_sessions[i];
     if (s->id != 0 && s->last_used < threshold) {
       fprintf(stderr, "Session %" INT64_X_FMT " (%s) closed due to idleness.\n",

mongoose.h

@@ -4647,21 +4647,42 @@ struct mg_str *mg_get_http_header(struct http_message *hm, const char *name);
 
 /*
  * Parses the HTTP header `hdr`. Finds variable `var_name` and stores its value
- * in the buffer `buf`, `buf_size`. Returns 0 if variable not found, non-zero
- * otherwise.
+ * in the buffer `*buf`, `buf_size`. If the buffer size is not enough,
+ * allocates a buffer of required size and writes it to `*buf`, similar to
+ * asprintf(). The caller should always check whether the buffer was updated,
+ * and free it if so.
  *
  * This function is supposed to parse cookies, authentication headers, etc.
  * Example (error handling omitted):
  *
- *     char user[20];
+ *     char user_buf[20];
+ *     char *user = user_buf;
  *     struct mg_str *hdr = mg_get_http_header(hm, "Authorization");
- *     mg_http_parse_header(hdr, "username", user, sizeof(user));
+ *     mg_http_parse_header2(hdr, "username", &user, sizeof(user_buf));
+ *     // ... do something useful with user
+ *     if (user != user_buf) {
+ *       free(user);
+ *     }
  *
- * Returns the length of the variable's value. If buffer is not large enough,
- * or variable not found, 0 is returned.
+ * Returns the length of the variable's value. If variable is not found, 0 is
+ * returned.
+ */
+int mg_http_parse_header2(struct mg_str *hdr, const char *var_name, char **buf,
+                          size_t buf_size);
+
+/*
+ * DEPRECATED: use mg_http_parse_header2() instead.
+ *
+ * Same as mg_http_parse_header2(), but takes buffer as a `char *` (instead of
+ * `char **`), and thus it cannot allocate a new buffer if the provided one
+ * is not enough, and just returns 0 in that case.
  */
 int mg_http_parse_header(struct mg_str *hdr, const char *var_name, char *buf,
-                         size_t buf_size);
+                         size_t buf_size)
+#ifdef __GNUC__
+    __attribute__((deprecated));
+#endif
+;
 
 /*
  * Gets and parses the Authorization: Basic header

src/mg_http_server.h

@@ -31,21 +31,42 @@ struct mg_str *mg_get_http_header(struct http_message *hm, const char *name);
 
 /*
  * Parses the HTTP header `hdr`. Finds variable `var_name` and stores its value
- * in the buffer `buf`, `buf_size`. Returns 0 if variable not found, non-zero
- * otherwise.
+ * in the buffer `*buf`, `buf_size`. If the buffer size is not enough,
+ * allocates a buffer of required size and writes it to `*buf`, similar to
+ * asprintf(). The caller should always check whether the buffer was updated,
+ * and free it if so.
  *
  * This function is supposed to parse cookies, authentication headers, etc.
  * Example (error handling omitted):
  *
- *     char user[20];
+ *     char user_buf[20];
+ *     char *user = user_buf;
  *     struct mg_str *hdr = mg_get_http_header(hm, "Authorization");
- *     mg_http_parse_header(hdr, "username", user, sizeof(user));
+ *     mg_http_parse_header2(hdr, "username", &user, sizeof(user_buf));
+ *     // ... do something useful with user
+ *     if (user != user_buf) {
+ *       free(user);
+ *     }
+ *
+ * Returns the length of the variable's value. If variable is not found, 0 is
+ * returned.
+ */
+int mg_http_parse_header2(struct mg_str *hdr, const char *var_name, char **buf,
+                          size_t buf_size);
+
+/*
+ * DEPRECATED: use mg_http_parse_header2() instead.
  *
- * Returns the length of the variable's value. If buffer is not large enough,
- * or variable not found, 0 is returned.
+ * Same as mg_http_parse_header2(), but takes buffer as a `char *` (instead of
+ * `char **`), and thus it cannot allocate a new buffer if the provided one
+ * is not enough, and just returns 0 in that case.
  */
 int mg_http_parse_header(struct mg_str *hdr, const char *var_name, char *buf,
-                         size_t buf_size);
+                         size_t buf_size)
+#ifdef __GNUC__
+    __attribute__((deprecated));
+#endif
+;
 
 /*
  * Gets and parses the Authorization: Basic header

test/Makefile

@@ -45,7 +45,9 @@ COMMON_FEATURE_FLAGS = \
 	-DMG_ENABLE_SNTP -DMG_SNTP_NO_DELAY_CORRECTION \
 	-DMG_ENABLE_HTTP_STREAMING_MULTIPART
 UNIX_FEATURE_FLAGS=-DMG_ENABLE_IPV6 -DMG_ENABLE_SSL
-CFLAGS = -W -Wall -Wundef -Werror -g -O0 -Wno-multichar -D__USE_MISC \
+# TODO: remove -Wno-deprecated-declarations once deprecated
+# `mg_http_parse_header()` is removed from mongoose.
+CFLAGS = -W -Wall -Wundef -Werror -Wno-deprecated-declarations -g -O0 -Wno-multichar -D__USE_MISC \
 	 $(COMMON_FEATURE_FLAGS) $(UNIX_FEATURE_FLAGS) \
 	 $(patsubst %,-I%,$(subst :, ,$(VPATH))) \
 	 -include unit_test.h -pthread $(CFLAGS_EXTRA)

test/unit_test.c

@@ -4941,12 +4941,34 @@ static const char *test_http_parse_header(void) {
       "xx=1 kl yy, ert=234 kl=123, "
       "uri=\"/?naii=x,y\";ii=\"12\\\"34\" zz='aa bb',tt=2,gf=\"xx d=1234");
   char buf[20];
+  char *buf2;
 
   ASSERT_EQ(mg_http_parse_header(&h, "ert", buf, sizeof(buf)), 3);
   ASSERT_STREQ(buf, "234");
+
   ASSERT_EQ(mg_http_parse_header(&h, "ert", buf, 2), 0);
   ASSERT_EQ(mg_http_parse_header(&h, "ert", buf, 3), 0);
   ASSERT_EQ(mg_http_parse_header(&h, "ert", buf, 4), 3);
+
+  buf2 = buf;
+  ASSERT_EQ(mg_http_parse_header2(&h, "ert", &buf2, 2), 3);
+  ASSERT(buf2 != buf);
+  free(buf2);
+
+  buf2 = buf;
+  ASSERT_EQ(mg_http_parse_header2(&h, "ert", &buf2, 3), 3);
+  ASSERT(buf2 != buf);
+  free(buf2);
+
+  buf2 = buf;
+  ASSERT_EQ(mg_http_parse_header2(&h, "ert", &buf2, 4), 3);
+  ASSERT(buf2 == buf);
+
+  buf2 = NULL;
+  ASSERT_EQ(mg_http_parse_header2(&h, "ert", &buf2, 0), 3);
+  ASSERT_STREQ(buf2, "234");
+  free(buf2);
+
   ASSERT_EQ(mg_http_parse_header(&h, "gf", buf, sizeof(buf)), 0);
   ASSERT_EQ(mg_http_parse_header(&h, "zz", buf, sizeof(buf)), 5);
   ASSERT_STREQ(buf, "aa bb");